1. Field of the Invention:
This invention relates generally to biomedical apparatus and more particularly to a flow-through resistivity cell attachable to a vascular diagnostic catheter for facilitating the measurement of blood resistivity.
2. Discussion of the Prior Art:
In certain diagnostic procedures, it is desirable to accurately determine the volume of a cardiac chamber. As is fully set out in the Salo et al Patent 4,686,987 and the Salo Patent 4,674,518, a technique called impedance plethysmography can be used to determine the ventricular volume of the heart. In making this measurement and computing this volume, a parameter which must be known is the resistivity of the patient's blood. In measuring resistivity, a sample of the patient's blood would first be drawn into a syringe and then transferred to a separate resistivity measuring cell of a known geometry where a resistance measurement would be taken. It is found, however, that the resistance measurement varies radically with temperature and that some means must be provided whereby the sample can be maintained at body temperature. An electrical heating element controlled by a body temperature measurement from a thermometer may be used. A delay is involved in waiting for the heater to bring the blood sample to body temperature, by slowing down the process and precluding real-time determination of chamber volume.
It is the principal object of the present invention to simplify the foregoing blood resistivity measurement apparatus and method so as to allow a rapid and accurate measurement of the blood resistivity to be taken, allowing a real-time computation of chamber volume.